1. Field of the Invention
The present invention relates to an encoding device, and more particular to an encoding device in which a gearing is incorporated such that signal generated thereof can be efficiently propagated.
2. Description of the Prior Art
In order to quickly and accurately move the cursor on the screen to execute the xe2x80x9cfunctionsxe2x80x9d of a program or to a certain position, an encoder is incorporated to generate signals that can be used to move the cursor vertically and horizontally. Conventionally, as shown in FIG. 3, a mouse generally includes an encoding mechanism which includes a tracing ball 1, and a pair of sensors 2 arranged perpendicularly to each other. Each sensor 2 includes a shaft 21, an encoding wheel 22 fixedly attached to an end of the shaft 21, and an optic transceiver 23, including a light emitter 231 and a light receiver 232, arranged adjacent to the encoding wheel 22. The shaft 21 includes a contacting portion 211 which is in contact with the tracing ball 1. Accordingly, the shaft 21 is rotated as the tracing ball 21 is moved. While the shaft 21 is rotated, the encoding wheel 22 is also rotated. Generally, the light emitter 231 keeps on emitting a light beam toward the light receiver 232, while the encoding wheel 22 is arranged between the lighter emitter 231 and the light receiver 232. As the encoding wheel 22 includes a plurality of slits 221 and mask 222 alternatively and peripherally arranged around the perimeter of the encoding wheel 22. As a result, when the encoding wheel 22 is rotated between the light emitter 231 and the light receiver 232, the light beam can freely pass through the slit 221, i.e. an xe2x80x9cOnxe2x80x9d signal, and be blocked by the mask 222, an xe2x80x9cOffxe2x80x9d signal. Therefore, the numbers of the On/Off signals can be used to calculate the rotations of the encoding wheel 22. After the signals are processed through the circuitry 3, the cursor on the screen can be easily and accurately moved and controlled.
In the conventional encoding mechanism, the vertical and horizontal movement or resolution of the cursor on the screen is proportional to the ratio between the tracing ball 1 and the encoding wheel 22, i.e. how many rotations of the encoding wheel 22 can be achieved when the tracing ball 1 rotates once.
In general, the resolution DPI (Dot Per Inch) can be expressed by the following formula:
DPI=25.4xc3x974xc3x97T/2xcfx80R,
in which
DPI: Resolution
T: Numbers of the slits on the encoding wheel
R: Diameter of the contacting portion of the shaft
In order to increase the resolutions, the following approaches have been suggested.
1. Reducing the diameter of the shaft, to increase the ration between the tracing ball and the shaft. However, the strength of the shaft is compromised when the diameter is reduced.
2. Increasing the slits and masks around the perimeter of the encoding wheel. However, this will inevitably increase the overall size of the encoding wheel and this is not acceptable.
3. Increasing the number of the slits and masks by reducing the size thereof. However, when the dimension of the slits and masks is reduced, the light emitter and receiver shall be changed accordingly, for example, to use a cap-type photocell. Otherwise, it is unlikely that the receiver can adequately pick up the light signal passing through the slits. In addition, when the numbers is increased, the dimension of the mask is also reduced. This makes the encoding wheel more vulnerable to damage. On the other hand, it is not cost-effective to make such an encoding wheel.
Another approach of the prior art is providing software which can convert the signal generated from the encoding wheel and the sensor such that the vertical and horizontal movement of the cursor on the screen can be increased. For example, if we set the original cursor movement corresponding to a signal unit is 1 unit, after the process of the software, the movement can be enlarged to 2 units, 3 units, or even 4 units, i.e. the cursor can move to an intended position faster than before. However, when the movement unit of the cursor is increased, the resolution of the cursor is accordingly decreased. It is hardly to use the cursor to control a tiny movement of the cursor.
It is an objective of this invention to provide an encoding device in which a gearing is incorporated such that signal generated thereof can be efficiently propagated without compromising the resolution thereof.
In order to achieve the object set forth, an encoding device in which signals generated thereof can be efficiently propagated in accordance with the present invention comprises a housing and a tracing ball rotatably arranged on said housing. An encoding assembly including a pair of encoding wheels is mechanically arranged adjacent to said tracing ball and driven by said tracing ball. Pair of light emitters and receivers is arranged respectively to opposite sides of each encoding wheel to generate signals. A gearing including first and second gears is arranged between the tracing ball and the encoding assembly such that number of said signals can be increased.